A variety of fan systems have been made and used over the years in a variety of contexts. For instance, various ceiling fans are disclosed in U.S. Pat. No. 7,284,960, entitled “Fan Blades,” issued Oct. 23, 2007, the disclosure of which is incorporated by reference herein; U.S. Pat. No. 6,244,821, entitled “Low Speed Cooling Fan,” issued Jun. 12, 2001, the disclosure of which is incorporated by reference herein; U.S. Pat. No. 6,939,108, entitled “Cooling Fan with Reinforced Blade,” issued Sep. 6, 2005, the disclosure of which is incorporated by reference herein; U.S. Pub. No. 2008/0008596, entitled “Fan Blades,” published Jan. 10, 2008, the disclosure of which is incorporated by reference herein; and U.S. Provisional Patent Application Ser. No. 61/034,254, entitled “Ceiling Fan System with Brushless Motor,” filed Mar. 6, 2008, the disclosure of which is incorporated by reference herein. Alternatively, any other suitable fans may be used in conjunction with embodiments described herein.
The outer tip of a fan blade or airfoil may be finished by the addition of an aerodynamic tip or winglet. Merely exemplary winglets are described in U.S. Pat. No. 7,252,478, entitled “Fan Blade Modifications,” issued Aug. 7, 2007, the disclosure of which is incorporated by reference herein; U.S. Pub. No. 2008/0014090, entitled “Cuffed Fan Blade Modifications,” published Jan. 17, 2008, the disclosure of which is incorporated by reference herein; and U.S. Pub. No. 2008/0213097, entitled “Angled Airfoil Extension for Fan Blade,” published Sep. 4, 2008, the disclosure of which is incorporated by reference herein. Other suitable structures that may be associated with an outer tip of an airfoil or fan blade will be apparent to those of ordinary skill in the art in view of the teachings herein. Alternatively, the outer tip of an airfoil or fan blade may be simply closed, or may lack any similar structure at all.
The interface of a fan blade and a fan hub may also be provided in a variety of ways. For instance, an interface component is described in U.S. Non-Provisional patent application Ser. No. 12/233,783, entitled “Aerodynamic Interface Component for Fan Blade,” filed Sep. 19, 2008, the disclosure of which is incorporated by reference herein. Alternatively, the interface of a fan blade and a fan hub may include any other component or components, or may lack any similar structure at all.
Fans may also include a variety of mounting structures. For instance, a fan mounting structure is disclosed in U.S. Non-Provisional patent application Ser. No. 12/203,960, entitled “Ceiling Fan with Angled Mounting,” filed Sep. 4, 2008, the disclosure of which is incorporated by reference herein. In addition, a fan may include sensors or other features that are used to control, at least in part, operation of a fan system. For instance, such fan systems are disclosed in U.S. Non-Provisional patent application Ser. No. 12/249,086, entitled “Ceiling Fan with Concentric Stationary Tube and Power-Down Features,” filed Oct. 10, 2008, the disclosure of which is incorporated by reference herein; and U.S. Provisional Patent Application Ser. No. 61/025,852, entitled “Automatic Control System for Ceiling Fan Based on Temperature Differentials,” filed Feb. 4, 2008, the disclosure of which is incorporated by reference herein. Alternatively, any other suitable mounting structures and/or fan systems may be used in conjunction with embodiments described herein.
In some installations, a ceiling fan is suspended from a ceiling structure by means of a vertical post or tube of some specified finite length. As the fan rotates at the bottom of this post or tube, any small imbalance of the rotating mass may result in a lateral force against the bottom end of the post or tube, which may tend to move the fan sideways. Because the mass is rotating, the direction of the resultant lateral force may also rotate at the same speed as the rotation of the fan, such that the fan may move in an orbital motion or rock in addition to rotating.
When a mass is suspended from a support by a vertical suspension member such as the post or tube described above, the assembly may have a natural resonant frequency at which any oscillation may be exaggerated. This frequency may vary based on a number of factors, including but not limited to the length of the supporting post or tube, the mass of the fan, and/or the mass of the post or tube. Because the length of the post or tube may not be determined until the time of installation, it may not be possible for the manufacturer of the product to predict the fan speed at which this resonance will occur in some scenarios. When the fan is rotating at the speed that matches the resonant frequency of the system, the lateral forces caused by the rotating mass may result in lateral and/or orbital oscillation of the fan.
In some settings, it may be desirable to minimize the oscillation of a fan in operation. One way of minimizing this oscillation may be to prevent the fan from rotating at the speed that corresponds to a resonant frequency of the assembly. Of course, preventing a fan from rotating at one or more certain speeds may yield other results, in addition to or in lieu of minimizing oscillation. To manually prevent a fan from rotating at one or more certain speeds may require the operator to observe the operation of the fan and avoid those settings at which it appears to oscillate.
It may also be possible, such as if the fan motor is controlled by a Variable Frequency Drive or other electronic speed control device, to program the control device so that it excludes certain frequencies from the speed control spectrum. Once this is done, as the manual control is adjusted, the control device may automatically select a slightly faster or slower speed, skipping past a speed that tends to cause the fan to oscillate. Performing this initial programming, however, may be time-consuming and may be beyond the capacity of some installers. It may also depend on visual observation to determine which speed or speeds should be excluded from the control spectrum to ensure best operation. Such observation may be imperfect and result in an incorrect programming of the control device.
While a variety of systems and techniques have been made and used to control fans and fan systems, it is believed that no one prior to the inventors has made or used the invention recited in the appended claims.
Reference will now be made in detail to various embodiments of the invention, examples of which are illustrated in the accompanying drawings. To the extent that specific dimensions are shown in the accompanying drawings, such dimensions should be regarded as merely illustrative and not limiting in any way. Accordingly, it will be appreciated that such dimensions may be varied in any suitable way.